make empty layout cells pulse while module is selected

src/ui/ShipLayoutDialog.cpp

@@ -1,6 +1,7 @@
 #include "ShipLayoutDialog.h"
 #include "ShipStatsPanel.h"
 
+#include <cmath>
 #include <functional>
 
 #include "DisplayName.h"
@@ -12,8 +13,10 @@
 #include <QMouseEvent>
 #include <QPainter>
 #include <QPushButton>
+#include <QElapsedTimer>
 #include <QScrollArea>
 #include <QSignalMapper>
+#include <QTimer>
 #include <QVBoxLayout>
 
 namespace
@@ -21,6 +24,13 @@ namespace
 
 const int kCellSize = 32;
 
+// Empty ship tiles pulse between this grey and white at 1 Hz while a module is
+// selected, to draw the player's attention to where modules can be placed.
+const double kTwoPi = 6.283185307179586;
+const int kPulseIntervalMs = 33;
+const int kEmptyCellGrey = 240;
+const int kPulseAmplitude = 15;
+
 std::vector<std::string> rotateMaskCW(const std::vector<std::string>& grid)
 {
     if (grid.empty())
@@ -68,6 +78,10 @@ public:
         , m_dialog(dialog)
     {
         setMouseTracking(true);
+        m_pulseClock.start();
+        m_pulseTimer = new QTimer(this);
+        m_pulseTimer->setInterval(kPulseIntervalMs);
+        connect(m_pulseTimer, &QTimer::timeout, this, [this]() { update(); });
     }
 
     void setGridData(const std::vector<std::vector<ShipLayoutDialog::CellInfo>>* grid,
@@ -87,6 +101,19 @@ public:
     {
         m_ghostModuleIdx = moduleIndex;
         m_ghostRotation = rotation;
+        // Only animate the empty-tile pulse while a module is selected.
+        if (moduleIndex.has_value())
+        {
+            if (!m_pulseTimer->isActive())
+            {
+                m_pulseClock.restart();
+                m_pulseTimer->start();
+            }
+        }
+        else
+        {
+            m_pulseTimer->stop();
+        }
     }
 
 protected:
@@ -100,6 +127,19 @@ protected:
         QPainter painter(this);
         painter.setRenderHint(QPainter::Antialiasing, false);
 
+        // While a module is selected, pulse empty tiles at 1 Hz around the base
+        // grey (kEmptyCellGrey +/- kPulseAmplitude). All empty tiles share the
+        // same phase, so compute it once.
+        QColor emptyCellColor(kEmptyCellGrey, kEmptyCellGrey, kEmptyCellGrey);
+        if (m_ghostModuleIdx.has_value())
+        {
+            const double seconds = m_pulseClock.elapsed() / 1000.0;
+            const double oscillation = std::sin(seconds * kTwoPi);
+            const int channel = kEmptyCellGrey
+                + static_cast<int>(std::lround(oscillation * kPulseAmplitude));
+            emptyCellColor = QColor(channel, channel, channel);
+        }
+
         for (int r = 0; r < m_rows; ++r)
         {
             for (int c = 0; c < m_cols; ++c)
@@ -131,7 +171,7 @@ protected:
                 }
                 else
                 {
-                    painter.fillRect(cellRect, QColor(240, 240, 240));
+                    painter.fillRect(cellRect, emptyCellColor);
                 }
 
                 painter.setPen(QColor(100, 100, 100));
@@ -241,6 +281,8 @@ private:
     std::optional<int> m_ghostModuleIdx;
     Rotation m_ghostRotation = Rotation::East;
     QPoint m_hoverCell = QPoint(-1, -1);
+    QTimer* m_pulseTimer = nullptr;
+    QElapsedTimer m_pulseClock;
 };